Abstract: 【Objective】The influence of pH on non-covalent forces and structure of myofibrillar protein heat-induced gel was studied. The relationship between gel non-covalent forces and gel structure was revealed. 【Method】 AA type broilers were slaughtered. The myofibrillar proteins were extracted from breast muscle. The myofibrillar protein solution and heat-induced gel with different pH values (5.0, 5.5, 6.0, 6.5, 7.0) were prepared. The potential on myofibrillar protein gel molecule presents the electrostatic interaction was measured by zeta potential instrument. The I760/I1003 showing the hydrophobic interaction of gel, the I850/I830 showing the hydrogen bonding of gel, and the secondary structure contents were calculated by analyzing the amide I Raman spectrum region, these were measured using Raman spectrometer. The particle size distribution was measured by a particle size analyzer. The microstructure was measured using scanning electron microscope.【Result】 From pH 7.0 to 5.0, Zeta potential value of the gel changed from -17.87 to -0.263 (P＜0.05), which show that the surface negative charges and the electrostatic interaction of myofibrillar protein gel had significant decline. The normalized intensity of 760 cm^-1 increased from 0.86 to 0.927, which show more Trytophan were buried and a general increase in hydrophobic interactions of myofibrillar protein gel. The normalized intensity of I850/I830 ratio decreased from 1.039 to 0.927, which indicated hydroxyl groups on the phenyl ring of tyrosine are to form hydrogen bonds with water molecules change to generate hydrogen bonds with other protein molecule residues. The interactions between myofibrillar protein molecules increased, and the interactions between myofibrillar protein and water therefore declined. From pH 7.0 to 6.5, the α-helix content of myofibrillar protein gel abruptly decreased from 59.96% to 55.24% (P＜0.05). The β-sheet content significantly increased from 15.83% to 19.44% (P＜0.05). β-turn and random coil content both significantly increased (P＜0.05). From pH 6.5 to 6.0, all structure content had no obvious change (P＞0.05). From pH 6.0 to 5.0, the α-helix content of myofibrillar protein gel significantly decreased from 51.61% to 16.76% (P＜0.05). The β-sheet content significantly increased from 22.23% to 48.93% (P＜0.05). β-turn and random coil content both significantly increased (P＜0.05). As the pH decrease, the α-helix content of myofibrillar protein gradually decreased, the β-sheet, β-turn and random coil content significantly increased (P＜0.05). From pH 7.0 to 5.0, particle size of myofibrillar protein gradually increased. D₁₀ increased from 13.4 μm to 48.4 μm, D₅₀ increased from 38 μm to 253 μm, D₉₀ increased from 236 μm to 805 μm. As the pH far away from neutral condition, the microstructure of gel changed to unordered and had smaller pore. Gel has disordered microstructure in pH 5.0, when has ordered structure at pH 7.0. The largest gel pore ware found at pH 5.0, the least were found at pH 7.0. pH had a highly negative significant correlation with electrostatic interaction and hydrophobic interactions (P＜0.01), and had a positive significant correlation with hydrogen bonding and α-helix content (P＜0.05). pH also led to negative significant change of β-sheet content (P＜0.05). These show that pH had a significant impacts on electrostatic repulsion, hydrophobic interactions, intermolecular hydrogen bonding and secondary structure. Electrostatic interaction, hydrophobic interactions and hydrogen bonding had significant correlation with secondary structure (P＜0.05), which indicated non-covalent forces had significant effects on secondary structure.【Conclusion】 Non-covalent forces and secondary structure content are significantly correlated with the pH valves. The reasons of gel α-helix reduction and β-sheet increases are the decreases of electrostatic interaction, and the increase of the hydrophobic interaction and the intermolecular hydrogen bonding of myofibrillar protein gel, as the pH far away the neutral conditions.

Key words: myofibrillar protein gel, electrostatic, hydrophobic, hydrogen bond, secondary structure, particle size, microstructure